With the help of flip-chip technology, it is possible to affix and bond surface wave components in a simple manner to a carrier (for example, a circuit board), to thereby arrange the component so it is mechanically protected, and to further reduce the size of the entire assembly. In addition, the piezoelectric substrate on which the surface wave element is realized in the metallized form is provided with solderable contacts on the surface. Corresponding cooperating contacts that provide solder pads are on a base plate, for example a ceramic multi-layer plate made from HTCC-ceramic. These solder pads are arranged by feedthroughs or plated through holes in the base plate or connected to it via metallic conductor paths, so that the electrical connection can ensue to the back side of the base plate. With the metallization facing down, the surface wave substrate is now mounted on the base plate and the connection between the solder pads and the solderable contacts on the chip is made with the aid of solder hunches-bumps.
The component structures on the chip thereby remain spaced from the base plate and are mechanically protected in the intervening space formed between chip and base plate. It is also possible to protect the component structures before the mounting of the chips on the base plate with the aid of a covering that, for example, can be generated in an integrated procedure from two-layer materials capable of being photostructured. The component structures are thereby better protected against environmental influences. To further seal the component, it is possible to cover the chip, for example, with a film or a layer that terminates tightly with the base plate. In addition, a radiofrequency shield of the surface wave component is possible with the aid of a metal layer or metal sub-layer.
With increasing miniaturization of surface wave components mounted with the flip-chip technique, the demand for base plates and the assembly technologies used is rising. For example, a larger number of bump connections are needed per unit of area that are often no longer realizable with reasonably priced methods. The application of bumps and conductor paths on the base plate occurs in a cost-effective manner by means of screen printing. Bump separations of up to a minimum of 250 μm and bump diameters or, respectively, conductor paths of a minimum of 80 μm can be produced by screen printing. Conductor path widths of a minimum of 80 μm are produced. If still smaller structures should be produced, an exact alignment of the structures on the base plate is no longer possible. This problem is aggravated in that the feedthroughs of the base plate are already produced in the green film phase of the ceramic. The green film is then transferred into the final hard ceramic by sintering. Admittedly, a shrinkage of the surface area that entails an error of more than 0.2% is associated with commonly used HTCC-ceramic. This makes a precise alignment of the bumps and conductor paths to be printed impossible.